At its inception radio telephony was designed, and used for, voice communications. As the consumer electronics industry continued to mature, and the capabilities of processors increased, more devices became available use that allowed the wireless transfer of data between devices and more applications became available that operated based on such transferred data. Of particular note are the Internet and local area networks (LANs). These two innovations allowed multiple users and multiple devices to communicate and exchange data between different devices and device types. With the advent of these devices and capabilities, users (both business and residential) found the need to transmit data, as well as voice, from mobile locations.
The infrastructure and networks which support this voice and data transfer have likewise evolved. Limited data applications, such as text messaging, were introduced into the so-called “2G” systems, such as the Global System for Mobile (GSM) communications. Packet data over radio communication systems became more usable in GSM with the addition of the General Packet Radio Services (GPRS). 3G systems and, then, even higher bandwidth radio communications introduced by Universal Terrestrial Radio Access (UTRA) standards made applications like surfing the web more easily accessible to millions of users (and with more tolerable delay).
As air interface technologies become more complex to meet the ever increasing demand for wireless voice and data services, the number of antennas being deployed at cell-tower sites, and other places, increases, and thus the number of radios required also increases. As a result, the number of coaxial cables between radios and antennas at each of these cites increase as well. As the number of radios and coaxial cables increases, the associated weight, cost and maintenance issues also increase. In some sites it is prohibitively expensive to deploy more coaxial cables to meet the new air interface needs.
Furthermore, radios in enclosures and remotely located radios are being deployed in ever increasing numbers for communication systems that provide the wireless voice and data systems. These radios can have a mean-time-between-failure (MTBF) on the order of 10 to 20 years, and therefore should be deployed in locations where they can be replaced when a failure occurs.
Some solutions have been proposed to address these issues. In order to provide a high level of quality of service, redundant systems can be put in place, and this means additional radios (transmitters, receivers, or transceivers) and even more coaxial cables. Thus, the number of radios in an enclosure can increase even further, and this also increases the number of coaxial cables, which can lead to cost, weight, and in some cases tower loading issues.
Another solution is to move the radios closer to, or combine them with, the antennas, thereby reducing or eliminating the length of the coaxial cables. That is, the radios and antennas can be enclosed or configured as much as practically possible into one integrated unit. While this solution may lead to less coaxial cable weight, it can lead to other problems, such as loading on towers (because in addition to the antenna weight, there is the added weight of the radio itself) and maintenance/repair of the components. Maintaining or replacing radios located on a tower can become prohibitively expensive as these are locations that are difficult to access. Active antennas, i.e., antennas with collocated radios, include digital devices, transceivers, power amplifiers (PA), low noise amplifiers (LNA) and other elements that can fail and/or experience performance degradation over time. If the antennas or antennas with collocated radios experience such performance issues, then failure of the radio can be very costly to replace as noted above.
As discussed above, to compensate for the possibility of failure of antenna/radio devices, it has been suggested that redundant devices be employed. While the digital components, receivers and other elements of the radio can be designed in a redundant configuration to significantly improve MTBF if needed, it is difficult to do this efficiently with the transmitter. Transmitters typically include analog, high power components (especially compared to digital components), and are fairly complex and expensive devices. Switches could be used to select standby transmitters should a transmitter fail, however, the switches themselves can fail and the standby transmitters provide no benefit under normal operation. Furthermore, in most systems, a certain number of standby transmitters would be needed to ensure adequate reliability. Standby transmitters should be kept “on” at a certain operational level, i.e., “warmed up,” to nearly instantaneously meet a shutdown condition of one or more of the “regular” transmitters, and thus would consumer additional power. Thus, the net result is an increase in weight and cost.
Accordingly, it would be desirable to provide a wireless voice/data communication system with reliable, substantially fail-safe redundant transmission capabilities that is low cost, and minimizes additional loading as much as is practically possible.